How Do You Choose What Scene To Purchase?You Keep Hard Copy?

Is it the Model, the Studs or Genre of sex? Also do you in todays age still download or just stream...if you download you must have a pretty big Collection with the size of some files? I myself choose mainly because of the Genre and sometimes if its a favourite Model I like. I do not download right now due to not External Hard Drive but I must get one soon. What size is best for EHD?